Reset text field to default when starting Blender
Use the window manager.
Related How to declare global variables for use in an addon that aren&#39;t stored in the blend file
For a session variable suggest using the window manager. Will always be default when new blender is openened. No window manager property is saved directly.
bpy.types.WindowMangager.password =  StringProperty(
        name=&quot;Password&quot;,
        description=&quot;Password&quot;,
        default=&quot;&quot;,
        subtype=&quot;PASSWORD&quot;)

SKIP_SAVE
Also look at using the skip save option of a property.
Force a Blender operator to always start with default values
Onload handler.
How to set blender default properties in addons?